Attention Deficit Hyperactivity Disorder (ADHD) is a common disorder of childhood associated with school failure, psychiatric comorbidity and psychosocial disability. Because family and twin studies suggest that ADHD has a substantial genetic component, several research groups have now begun molecular genetic studies of the disorder. These studies have already produced two replicated findings: one showing an association between ADHD and the D4 dopamine receptor gene and the other between ADHD and the dopamine transporter gene. Another well replicated feature of ADHD is its pattern of cognitive dysfunction along with structural and functional abnormalities in frontal-subcortical neural networks. Notably, the areas of cognitive deficit seen in ADHD are moderately heritable, as are the volumes of implicated brain structures. We are thus proposing a networking grant which seeks to establish collaborative partnerships among scientists who study basic behavioral processes associated with attention deficit hyperactivity disorder (ADHD) and those who study the genetics of the disorder. Thus, there are three main facts that underlie the present proposal: 1) ADHD is heritable; 2) it is associated with a pattern of cognitive dysfunction; and 3) it is associated with structural and functional brain abnormalities. These facts lead us to believe that it will be fruitful to create a network of researchers studying these domains of inquiry. The main aims of the proposed network are: 1) to provide a venue for basic and clinical investigators to initiate and explore the potential of research collaborations that focus on genetics and cognition in ADHD; 2) to identify cognitive phenotypes suitable for molecular genetic studies of ADHD; 3) to identify neuroimaging phenotypes suitable for molecular genetic studies of ADHD; 4) to design research projects aimed at finding genes that mediate the neuropsychological and neuroimaging abnormalities associated with ADHD; 5) to identify candidate genes that mediate these phenotypes; 6) to design protocols that use neuropsychological and neuroimaging methods to clarify the functional significance of gene variants implicated in the etiology of ADHD; and 7) to encourage junior investigators to develop research careers that integrate the domains of genetics, cognition and neuroimaging in ADHD.